Until last December, a very large majority of the scientific community and most politicians would have agreed that the scientific evidence of human- induced climate change was unequivocal and that the sole question was whether the world's political leaders could agree in Copenhagen to meaningful, legally binding greenhouse gas emission reduction targets. But, as we now know, the negotiations only produced an aspirational target of limiting the global mean surface temperature to no more than 2 degrees C above pre-industrial levels and an accord that does not bind any country to reduce its emissions.

Since then, there have been reported errors and imprecise wording in the Fourth Assessment report of the Intergovernmental Panel on Climate Change (IPCC), issued in 2007. These include the hyped statement that Himalayan glaciers would melt by 2035 or earlier (the IPCC admitted that this was an outright error and not evidence-based); that agricultural production in some North African countries would decrease by up to 50 percent by 2020 (the synthesis report failed to include the nuances and more detailed discussion in the underlying chapter); and that over half of the Netherlands was below sea level, rather than a quarter. (This was largely a definitional issue — the Dutch Ministry of Transport uses the figure 60 percent below high water level during storms.)

These errors or imprecise wording in the IPCC's 2007 Working Group II report, coupled with the issues surrounding the hacked e-mails and temperature data from the University of East Anglia, have provided the climate skeptics and some in the media with ammunition to undermine public confidence in the conclusions of the IPCC and climate science in general.

Clearly, the language in the leaked e-mails could suggest that the scientists may have inappropriately manipulated the data to support the theory of human-induced climate change and attempted to suppress other data that contradicts this theory. That is why I applaud the University of East Anglia — affiliated with the Tyndall Center for Climate Change Research, where I work as strategic director — for rapidly establishing an independent review of the whole issue. But to suggest that the hacked e-mails or the identified inaccuracies in the IPCC's Working Group II report undermine the broad evidence that the Earth's climate is changing due to human activities — or that any talk of carbon emissions cuts should be suspended — is simply untenable.

Recently, the UK Royal Society, the National Environment Research Council and the UK Meteorological Office issued a joint statement not only supporting the findings of the 2007 IPCC report, but showing that recent scientific information further strengthens those conclusions. The statement concluded that these agencies could not emphasize enough the body of scientific evidence that underpins the call for action now. Also, a statement from 11 science academies in developed and developing countries concluded that climate change is real, and that we need to prepare for the consequences, and urged all nations to take prompt action to reduce their greenhouse gas emissions.

So let me return to the issue of the IPCC, which is one of the most rigorous scientific review bodies in existence. Many thousands of scientists have dedicated their time to preparing and reviewing the most comprehensive and authoritative assessments of climate science available. In addition, governments from around the world have reviewed and approved the IPCC's key findings. The reports undergo two rounds of peer review, and the policymakers' summaries of the working groups are then subjected to a word-by-word approval of all governments in the presence of the chapter lead authors.

In many cases, the IPCC is very conservative in its statements, e.g., the projections of sea level rise reported in Working Group I were based on contributions from thermal expansion of the oceans and the melting of mountain glaciers, but did not contain a contribution from the melting of the Greenland ice sheet, due to an inadequate understanding of the current rate of melting.

Some would say that only four mistakes or imprecise wording have been found in the 1,000-page Working Group II report, and none in working groups I and III, and so would ask: Is there really a problem? But given that each of the mistakes overstated the implications of climate change, it is critical to regain any lost trust from the media, public, governments, and private sector. The IPCC could start by posting all errors — accompanied by explanations of how they were made — on its website.

I see no evidence that the authors purposely overstated the potential impacts from climate change in an effort to convince the public of the seriousness of the threat. The threat is serious enough without the need to hype the issue. But the expert and government peer-review process should have caught these inaccuracies and careless wordings. The vast amount of attention in the print and TV media, especially in the UK, has clearly left some of the public confused, if not skeptical.

The challenge now is to regain any lost trust through a continuing re-examination and restatement of the evidence, clearly identifying what we know and what is still uncertain. It is critical that the public understand the issue of climate change, given the need to both mitigate and adapt in a cost-effective and socially responsible manner.

So does the IPCC process need to be significantly revised? I would argue no, that the IPCC is more than capable of conducting rigorous and reliable assessments in an open, transparent, and inclusive manner. But the IPCC needs to regain its full and deserved credibility. The procedures for the selection of authors and review editors and the peer-review process and approval of reports are all sound. What is needed is to tighten up the implementation of these procedures, coupled with training of authors and review editors. The selected authors need to represent the full range of credible views, including those of the skeptics, and must ensure that all statements are based on sound science and that the citations used contain convincing evidence.

The IPCC should consider shorter reports focused on the key issues, rather than the all-encompassing reports that have become the norm. Authors, peer reviewers, and the working group secretariats need to be absolutely rigorous in ensuring that all conclusions are backed up by evidence, with an accurate assessment of how good the evidence is, and that all of the citations are valid. Gray literature — i.e., the use of non-peer-reviewed literature — can and should be used as long as it is evidence-based and available to the peer reviewers for evaluation.

One criticism often aimed at the IPCC is that it is inflexible and unable to conduct rapid response assessments of new evidence due to the requirements of two rounds of peer review involving experts and governments. One solution to this weakness is to complement, not replace, the IPCC by developing a "peer-reviewed" Wikipedia that can continually update the evidence and synthesize the findings and note where the new evidence strengthens, modifies, or undermines previous conclusions.

In my opinion, there is no doubt that the evidence for human-induced climate change is irrefutable. The world's leading scientists, many of whom have participated in the IPCC, overwhelmingly agree that what we're We must not allow the skeptics to derail the political will to safeguard the planet. experiencing cannot be attributed to natural variation in the climate over time, but is due to human activities. And they also agree that if we do not act, climate change will continue apace with increasing droughts, floods, and rising seas, leading to major damaging impacts to the natural world (loss of species and critical ecosystem services) and society (displaced human populations).

There is no doubt that the atmospheric concentration of greenhouse gases has increased significantly over the past 150 years primarily due to human activities. These gases are radiatively active and absorb and trap outgoing infrared radiation from the Earth's surface and hence, based on simple physics, the Earth's atmosphere must respond by warming. The only issue is by how much and when.

The IPCC concluded that the global temperature data and analyses are robust, with evidence of increasingly variable and extreme temperatures, coupled with increasingly severe weather events, heat waves, floods, and droughts. While a number of scientists argue that some of the land temperature data is contaminated and unreliable because of the urban heat-island effect and movement of observational sites, ocean data — as well balloon and satellite data — also show an increasingly warmer world. These data sets are clearly free from any potential contamination from any urban heat island effect.

In addition, the evidence for a changing climate over the past 100 years also comes from observed changes in retreating mountain glaciers throughout most of the world, a decline in the extent and thickness of Arctic sea ice, melting of the Greenland ice sheet, changes in precipitation patterns, and changes in vegetation and the behavior of wildlife. Yet despite this accumulating evidence, the challenges of the skeptics must be fully addressed.

The key question is the cause of the observed changes in temperature. The IPCC concluded that it is more than 90 percent certain that most of the observed changes over the past 50 to 60 years are due to human activities and that the changes cannot be explained by known natural phenomena.

Future increases in greenhouse gas concentrations are projected to be accompanied by increased climate variability and more extreme climatic events, leading in general to adverse impacts on agriculture, water quantity and quality, coastal erosion, loss of biodiversity, and degradation of ecosystem services. Developing countries will be the most vulnerable. Therefore, it is clear that climate change is not only an environmental issue, but a development and security issue.

All major emitters of carbon dioxide and other greenhouse gases need to rapidly and cost-effectively transition to a low-carbon economy, in both the production and use of energy and the management of forests and agricultural lands. In order to ensure food, water, and human security, and to protect the world's biodiversity, the goal should be to limit the global average temperature rise to 2 degrees C (3.6 degrees F) above pre-industrial levels. This will require a peak of global emissions of all greenhouse gases by around 2015, and at least a 50 percent reduction in global emissions by 2050, relative to 1990. Without concerted action now, the world will be faced with temperature increases far in excess of 2 degrees C, with unthinkable impacts.

An equitable and substantive post-Kyoto agreement is essential if the target of 2 degrees C is to be realized. Industrialized countries must demonstrate leadership, and provide developing countries with technical and financial assistance to reduce their greenhouse gas emissions while they address the critical issues of poverty and hunger.

Given the limited success at Copenhagen, 2010 is a critical year for the world's political leaders to unite in the fight against climate change. Strong and visionary political leadership will be essential. We must not allow the skeptics to use the incident at the University of East Anglia or the mistakes in the IPCC report to distract us or derail the political will to safeguard the planet.Click here to read a contrasting view from IPCC critic Roger A. Pielke Jr.